When we were first dating, I used to visit my then bf at his home and he would drive me home later in his car (which was a bit of an old banger). One day I was there and bf's car wouldn't start. He asked his dad if he could borrow his car to take me home (I lived about 30mins away). FiL said yes no problem. MiL piped up to say "the car is half mine, and I say no". I was gobsmacked! My bf did borrow the car and my FiL later apologised for the way MiL had spoken. She made various other snide comments to me over the years. She was one of those women who lived through her DCs and thought I was taking her precious boy away from her.
She was very upset that we chose to have our wedding reception in a church hall. MiL liked to show off to other people and wanted us to have it at some posh expensive venue (even though she wasn't contributing any money towards it).
She turned up at my wedding wearing an almost white dress. I had the last laugh because lots of people were talking about her behind her back and saying how inappropriate it was.
When DH and I had our first dance, we'd forgotten to tell the DJ what song we wanted played. Instead of checking with us she decided for herself what it would be. Totally screwed up the wedding video because it was the same song that we'd chosen for the intro.
After the photos were taken, we should have gone inside to welcome all our guests into the reception, but she organised for us to go into the sit down area and have loads of extra photos with her 'great aunt Mary', so all our guests had to be welcomed in by my parents instead. Little things, but they all added up to become one huge irritation.
When we had difficulty conceiving, we had tests done and it was found that DH had an extremely low sperm count. She insisted on bringing round magazine articles she'd found about female infertility.